1. Field of the Invention
The present invention relates to a flying splice knife for cutting a moving web. More specifically, the present invention relates to a flying spice knife for cutting a moving web in which a plurality of individual blade sections are mounted at predetermined angles with respect to a support member whereby the plurality of blade sections are simultaneously engageable with the moving web.
2. Description of Related Art
A "flying splice" of an expiring wound roll of flexible web material to another wound roll of web material allows for continuous operation of web handling equipment without stopping or slowing a machine to join web material together from two different rolls. The success rate of making flying splices that do not fail or clog machine parts is critical to the efficiency of web-handling equipment. For this reason, equipment is required to sever a web and form a splice. The equipment is constantly monitored and worked on to minimize operating costs and improve efficiency.
A typical mechanism for making overlapped flying splices is shown in FIGS. 9-15. In FIG. 9, an expiring wound roll 71 of web material 72 is shown being unwound by rotation on spindle A past an idler roller 74 leading to a processing machine (not shown). As the material or web from expiring roll 71 is exhausted, a turrent 70 interchanges a new roll 76 rotating on spindle B with the expiring roll 71 by rotating the turrent 70 around a turrent axis 78 in a clockwise direction. Before the new roll 76 is interchanged with the expiring roll 71, a two-sided adhesive tape 80 is placed along the leading edge 82 of an unspliced web of the new roll 76. A rubber paster roller 84 is used to compress the two webs together and is shown positioned in a retracted position to allow the turrent 70 to rotate.
FIG. 10 shows the turrent 70 rotated 180.degree. in order to position the expiring web 72 under one of two flying splice knives 86, 87. Each knife 86, 87 is on opposite sides of turrent 70 and positioned between two rotatable support rollers 88. The knife 86 is shown in a "ready to fire" position. After the turrent 70 is repositioned through the above-mentioned 180.degree. rotation, the new roll 76 is accelerated to rotate at the same outer surface speed as the web 72 while the paster roller 84 is moved to the "ready to fire" position.
FIG. 11 shows the splicing mechanism in action. When the expiring roll 71 reaches a minimum diameter, the severing and splicing sequence is triggered, thereby firing the paster roller 84 against the new roll 76 which sticks the expiring web 72 to the new roll 76 as the two-sided adhesive 80 passes through a nip formed by the paster roll 84 pressed against the new roll 76. Almost simultaneously, the flying splice knife 86 is fired downward into the expiring web 72 by a high speed pneumatic or hydraulically actuated firing mechanism 90 at an angle perpendicular to a longitudinal axis of the web 72. The web 72 severs when the tension of the web 72 over the knife 86 becomes large enough to tear the web 72 in a crosswise direction. After an expired core located at the center of the expired roll 71 is removed and replaced with a fresh wound roll on spindle A, the severing and splicing cycle is ready to be repeated, this time using the remaining flying splice knife 87 after another 180.degree. clockwise rotation of the turrent 70.
FIG. 12 shows a more detailed view of a conventional flying splice knife 92. The width of the knife blade can vary widely, but is typically 100 inches (254 cm) in length as shown at l.sub.1, The knife 92 is oriented with its firing or z-axis 94 and its cross direction or y-axis 96 perpendicular to the web surface 98 and web travelling direction 100, respectively. A velocity of the web 98 typically ranges between 500 and 3000 feet per minute (fpm) (254 cm/sec to 1524 cm/sec). The velocity of the knife 92 typically ranges between 300 and 700 feet per minute (152.4 cm/sec to 355.6 cm/sec) depending upon the configuration of the actuator mechanism 90 and the size and type of hydraulic or pneumatic cylinders used to energize the actuator mechanism. Knife velocity is varied by changing the cylinder pressure Typically, knives have a 4 to 6 inch (10.16 cm to 15.24 cm) total firing distance and reach full speed after 2 to 3 inches (5.08 cm to 7.62 cm) of travel. These knives are generally equipped with triangular-shaped teeth 102 with sharpened bevel-cut edges. Tooth width and length range between 3/8 inch and 3/4 inch (0.9525 cm to 1.905 cm) shown at w1, and l.sub.2, respectively.
FIG. 13 illustrates a typical web tear resulting from the conventional flying splice knife 92. The machine direction 104 and knife orientation 106 are labeled. Initial contact of knife teeth tips 103 with the web 98 results in generating machine direction tears 108. The length l.sub.3 of these tears is typically 7 to 14 inches (17.78 cm to 35.56 cm) depending upon web speed, knife speed, web tension, substrate type, and number of teeth. In other words, the greater number of teeth, the longer the tears produced.
A second stage of the severing action is produced by the edges of the teeth when the pressure at the tip 103 of each tooth 102 becomes large enough to push the entire knife tooth 102 through the web. The time required for the knife tooth to pass through the web forms triangular shaped web tears 110. A spliced end 112 of the web 98 is sent through the processing machine. A non-spliced end 114 of the web 98 does not pass through the process and is that portion which would be found on the expiring roll 71.
FIG. 14 illustrates how the triangular tear 110 is generated by a conventional knife tooth 102, wherein the time tk required to complete one tooth cut is equal to the time required for the knife tooth 102 to travel a distance equal to dk, the tooth height. The time, tk, can be expressed as: EQU tk=dk/Vk (1)
where Vk is equal to the knife tooth velocity. The distance dw the web travels in this amount of time is equal to the length of the tear. The distance, dw, can then be expressed in terms of Vk and Vw, the web velocity and dk, the tooth height, by equation 2. ##EQU1##
Making the height dk of the tooth smaller by increasing the point angle to make the tooth blunter will act to shorten the tear triangle 110 but will also produce longer machine direction tears 108 by making it harder for the tooth 102 to penetrate through the web 98. Providing sharper, more pointed teeth will act to deflect the web 98 less which reduces the length of the machine direction tears 108 but increases the length of the tear triangle 110.
If a coating process performed on a spliced web at 118 as shown in FIG. 15 requires multiple cycles of wetting and drying on both sides of the web, the flying splices may fail. For example, ribbons 116 (shown as tear triangles 110 in FIG. 13) made by the tearing action of the knife allows excessive amounts of coating to accumulate between and under these ribbons 116 causing the ribbons to become weak and breakable away from the remaining web 98. The machine direction is again shown by arrow 104.
If this heavy coating area cannot be dried completely, the ribbon area will also become stuck to various machine parts such as a rod coater backing roll, resulting in the destruction of the splice and a web break.
Next, weakened splice ribbons 116 and other web fragments loosely attached to the web 98 as a result of web severance by the knife tend to easily tear off and clog drier nozzles or become caught in the coater rod causing coating application defects in the product.
Accordingly, a need in the art exists for a flying splice knife for severing a moving web which results in a relatively smooth finished edge which will in turn prevent numerous problems described above in connection with the conventional flying splice knives.